Method and apparatus for curing tires

ABSTRACT

A method for curing a tyre includes the steps of closing the tyre in a mould, heating at least one lower hot table, at least one upper hot table, and at least one annular hot table to transmit heat to the tyre. The at least one lower hot table, the at least one upper hot table, and the at least one annular hot table are associated with the mould. The at least one annular hot table is thermally-connected to a circumferential development of the mould. A quantity of heat provided to the at least one lower hot table is different from a quantity of heat provided to the at least one upper hot table. An associated apparatus includes a mould; at least one lower, upper, and annular tables; and devices for supplying one or more heating fluids to the at least one lower, upper, and annular tables.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry under 35 U.S.C. §371 fromInternational Application No. PCT/EP00/11943, filed Nov. 29, 2000, inthe European Patent Office, the contents of which are relied upon andincorporated herein by reference; additionally, Applicant claims theright of priority under 35 U.S.C. §119(a)-(d) based on patentapplication No. 99830771.4, filed Dec. 13, 1999, in the European PatentOffice; further, Applicant claims the benefit under 35 U.S.C. §119(e)based on prior-filed, copending provisional application No. 60/179,393,filed Feb. 1, 2000, in the U.S. Patent and Trademark Office.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for curing tyres, comprisingthe phases of closing a tyre to be cured in the moulding and curingcavity of an appropriate mould and of heating the lower, upper andlateral walls of said mould to transmit heat to the tyre.

The invention further relates to a device for curing tyres, comprising:a curing mould defining a moulding and curing cavity suitable to receivea tire being processed at least a lower hot table situated adjacently toa lower wall of said curing mould; at least an upper hot table situatedadjacently to an upper wall of said curing mould, at least a peripheralhot table situated around the lateral development of the moulding andcuring cavity; devices for supplying heating fluid in said hot tables.

2. Description of the Related Art

Production processes for vehicle tyres provide for each tyre, afterhaving been assembled in all its components, to be subjected to amoulding and curing process during which the tyre itself is made toadhere with adequate pressure against the inner walls of a mouldingcavity, and to the administration of heat to determine, with thepolymerisation of the elastomeric material whereof it is composed, itsdefinitive geometric and structural stabilisation.

With particular reference to the curing of tyres for vehicles, for thispurpose the use of so-called centripetal devices is widespread. Examplesof such devices are for instance described in the following patents:U.S. Pat. No. 5,676,980, EP 123,733, EP 170,109 and EP 459,375.

Devices of this kind are generally arranged with the axis of the mouldin vertical position and the median, or equatorial plane, of the mouldhorizontal relative to the ground; the moulding cavity is essentiallydefined between two annular cheeks, respectively inferior and superiorwith reference to said plane, coaxially arranged to form the exteriorsurfaces of the sidewalls of the tyre. To the cheeks is combined a crownof sectors arranged circumferentially around the geometric axis of themould, coinciding with the axis of rotation of the tyre, to shape thetread band of the tyre, define therein a series of indentations and/orgrooves arranged in varied ways according to a desired tread design.

The lower cheek is generally fixed relative to a base, whereas the uppercheek, engaged to a so-called lid movable vertically, can be translatedaxially relative to the lower cheek.

The circumferential sectors, in turn, are slidingly engaged to asector-holder ring which is integral, depending on the case, either withthe lid or with the base. More in particular, the sectors are movablealong respective generatrices of a cone frustum shaped surface providedin the sector-holder ring. Simultaneously with the mutual axialactuation between ring and sectors, the latter are simultaneouslytranslated radially to the axis of the mould, between an open conditionwherein they are circumferentially distanced from each other, i.e.radially removed from the outer circumferential surface of the tyrecontained in the mould, and a closed condition wherein they are radiallyapproached and mutually matching in correspondence with the respectivecircumferentially opposite edges.

Hearing devices are further provided for transmitting a pre-determinedquantity of heat to the tyre closed in the moulding cavity, in order todetermine its adequate curing.

These heating devices essentially comprise a plurality of so-called “hottables” positioned around the components that define the moulding andcuring cavity. For the purposes of the present description, the term“hot table” is taken to mean a structural part of the curing unit,presenting at least a cavity, different from the moulding and curingcavity, able to be supplied with any suitable heating fluid.

More specifically, a lower hot table, located immediately underneath theaforesaid lower cheek, an upper hot table, located adjacently above theupper cheek, and an annular hot table associated with the sector-holderring and extending around the sectors themselves, are provided.

Whilst the upper and lower hot tables are supplied with fluid, usuallysteam, at the same temperature, in the order of 175° C. by way ofindication, the fluid injected into the annular hot table can have atemperature in the order of 185° C., or in any case exceeding thetemperature of the fluid injected into the lower and upper chambers.

This greater temperature is selected in consideration of the fact thatthe crown of the tyre, in contact with the sectors, has a greaterthickness than the thickness of the sidewalls and includes the beltstructure, i.e. a pack of at least three strips of rubber-coated fabric,textile or metallic, and thus requires a greater quantity of heat toreach, in the same cycle time, substantially the same degree of curing.

In particular, it is also known document GB 1,118,005 disclosing anapparatus for embossing a pattern in the tread band of a pneumatic tyreof the type described above which may supply steam at differenttemperatures to the chambers of the hot tables in dependence of thethickness of the parts of the tire to be cured.

It has always been deemed that the known curing method described aboveallowed to fabricate tyres with a homogeneous degree of curing or, atleast, with any inconsistencies symmetrically distributed relative tothe equatorial plane in relation to the different thickness between thedifferent areas of the tyre and to the different size of the carcass insaid areas.

After the premise above, it should be noted that the tyre industryconstantly strives to search for continuous improvements both of theperformance offered by the tyre in operation and of the degree ofuniformity of the product in order continually to restrict the band oftolerability of the values of the viscosity and elasticitycharacteristics of the cured tyre which deviate from the pre-determinedideal value.

In this search for continuous improvements, sustained by an accurateanalysis of the product, the Applicant has found that the tyre oftenbehaves differently, to a greater or lesser extent, when engaged in acurve in a given direction from the way it does when engaged in theopposite direction.

This inconsistent behaviour was initially and hastily attributed totolerable quantitative differences between the geometric characteristics(thickness, height and profile) of the two semi-finished products thatconstituted the opposite sidewalls of the tyre or to small variations inthe geometric characteristics of the compound of the two sidewalls whichtook place during the sidewall preparation (straining or calendering)process.

SUMMARY OF THE INVENTION

However, as manufacturing processes and process control systemsimproved, this notion no longer seemed convincing: the Applicant thusintuited that perhaps the two sidewalls of the tyre, while having thesame chemical composition, and specifically the same quantity of thedifferent ingredients in the formula of the compound, as well as thesame geometric dimensions, could yet present some diversity in thephysical and or viscous-elastic properties of the compound, notperceivable at first glance, caused by or in any phase of the tiremanufacturing process.

The Applicant found that tyres with the aforesaid inconsistent behaviourin curves presented sidewalls mainly with a different value of theelasticity module and intuited that such difference in value was to belinked to a different degree of curing of the sidewall compound. TheApplicant then understood that the known curing method, with the intentof obtaining a tyre with homogeneous characteristics, in particular withregard to the sidewalls, had transferred the concept of homogeneity alsoto the temperatures whereas the steam was supplied to the hot tables ofthe curing mould.

In practice, instead, also for the specific lay of the curing mould withthe cheeks radially superposed and parallel relative to the ground, theimposition of a homogeneous supply temperature for the two tables, lowerand upper, did not translate into a homogeneous quantity of heatabsorbed by the sidewalls of the tyre

Indeed, the equality of the temperatures of the steam introduced intothe lower and upper hot tables, led in fact to a non-homogeneous thermalcondition of such tables since the lower hot table, transmitting andirradiating heat upwards, contributed to heating the upper hot tablewith the consequent greater heat absorption thereby.

This different heat absorption by the two hot tables, and by thecorresponding cheeks of the mould, entailed a different quantity of heattransferred to the sidewalls of the tyre and hence a different degree ofreticulation between the two sidewalls, with the consequent diversity inmechanical and behavioural characteristics observed in the finished tire

In accordance with the invention, the problem has been solved with adifferent heating of the two hot tables, lower and upper, dimensionedtaking into account the transmission of heat between the different partsof the curing device, in order to determine an equal absorption of heatby the two sidewalls subjected to curing It was further noted that thisway of proceeding allows also to improve the curing homogeneity of thecircumferential portions of tread on the shoulders of the tyre.

In a first aspect, the invention thus relates to a method for curing atyre entailing the use of curing mould presenting a moulding and curingcavity suitable for receiving a tyre being processed, a lower hot tableand an upper hot table axially opposed and suitable for operating onrespective sidewalls of the tyre and at least an annular hot tablepositioned around the circumferential development of the moulding andcuring cavity, comprising the following phases:

-   -   closing a tyre to be cured in said moulding and curing cavity;    -   heating the lower, upper and annular hot tables to transmit heat        to the tyre, wherein different quantities of heat are        transferred to said hot tables during said heating phase, in        order to cure the tyre homogeneously.

In accordance with a first aspect of the present invention, it was foundthat it is possible to achieve unexpected improvements in the tyrecuring process, particularly in terms of homogeneity in the entyrestructure of the cured tyre, if the hot tables, or different portionsthereof, are supplied independently with different heat inflows, and inparticular if the temperature of the steam or other heating fluid fedinto the lower hot table is higher than the temperature of the heatingfluid fed into the upper hot table.

In accordance with this aspect of the invention, a method for curing atyre is characterised in that the tyre heating phase is carried outsupplying the lower hot table with heat in a greater quantity than theheat supplied to the upper hot table.

Alternatively or in combination with this aspect, also the heating ofthe annular hot table is performed by supplying its lower portion withheat in greater quantity than the heat supplied to its upper portion.

Preferably, the heating of the hot tables is effected by supplying aheating fluid to the hot tables themselves, and still more preferably,the fluid supplied to the lower hot table and/or to a lower portion ofthe annular hot table has a greater temperature than the temperature ofthe fluid supplied to the upper hot table and/or respectively to anupper portion of the annular hot table itself.

For this purpose, the fluid supplied to the lower hot table canadvantageously also be supplied to a lower portion of the annular hottable, whilst the fluid supplied to the upper hot table canadvantageously also be supplied to an upper portion of the annular hottable.

According to a preferential embodiment, the fluid supplied to the lowerhot table comprises dry saturated steam at a temperature ranging between155° C. and 165° C., whilst the fluid supplied to the upper hot tablecomprises dry saturated steam at a temperature ranging between 148° C.and 158° C.

In one of its different aspects, the invention relates to a device forcuring tyres for wheels of vehicles, characterised in that the devicesfor supplying the fluid supply differentiated portions of said hottables in mutually independent fashion, and in particular, they supplythe lower hot table with fluid at a different, preferably higher,temperature, than the temperature of the fluid supplied to the upper hottable.

Preferably, the annular hot table is divided into at least a lowercavity and at least an upper cavity according to a diametrical planerelative to the moulding and curing cavity, so that the fluid supplyingdevices can supply the lower cavity of the annular hot table with fluidat different, preferably higher, temperature, than that of the fluidsupplied to the upper cavity of the annular hot table itself.

For this purpose it can preferably be provided for the lower cavity ofthe annular hot table to be in fluid communication with the lower hottable, whilst the upper cavity of the annular hot table is in fluidcommunication with the upper hot table.

According to a preferential embodiment of the invention the fluidsupplying devices further comprise at least an injection conduitdischarging into the interior of the moulding and curing cavity and atleast an extraction conduit originating from the same moulding andcuring cavity.

In accordance with a different preferential embodiment of the invention,the lower cavity and the upper cavity of the annular hot table arerespectively obtained in an upper containment portion and a lowercontainment portion of a containment structure; preferably, saidcontainment portions are mutually movable between a closed conditionwherein they are in mutual contact, mutually matching preferably on adiametrical plane of the moulding cavity, and an open condition whereinthey are mutually axially distanced.

More in particular, in the closed condition the upper containmentportion and the lower containment portion can advantageously mutuallymatch according to a median equatorial plane of the moulding and curingcavity.

In accordance with a further aspect of the invention, which can also beexploited independently of the above description, the mould comprisesthe usual crown of sectors divided into a plurality of lower radialsectors and a plurality of upper radial sectors respectively engaged insaid lower and upper containment portions, circumferentially distributedaround the geometric axis of said moulding and curing cavity; each ofsaid sectors comprises a support body slidingly engaged in thecorresponding containment portion to be selectively moved,simultaneously with the mutual axial motion of the containment portions,between a closed condition, wherein said sectors are mutually approachedand matching to define the moulding and curing cavity, and an opencondition wherein the sectors of the same plurality are radially removedrelative to the aforesaid geometric axis, circumferentially distancedfrom each other, and axially distanced relative to the sectors of theopposite plurality, and each of said sectors further comprises at leasta moulding die removably engaged to the support body.

Preferably, in the closed condition the lower sectors and the uppersectors mutually match according to the equatorial median plane of themoulding and curing cavity.

It is also preferable for each of said sectors to be operatively engagedin the annular containment portion, slidingly guided along acorresponding cone frustum shaped surface obtained on the inner surfaceof its containment portion, respectively lower and upper, to determinethe mutual radial removal of said sectors.

Preferably, to each support body are engaged at least two of saidmoulding dies able to slide on the support body itself and mutuallymovable according to a circumferential direction relative to themoulding and curing cavity.

Each of said moulding dies advantageously presents a circumferentialextension corresponding to at least a pitch of a tread design to bedefined on the tyre being manufactured.

In accordance with this inventive aspect of the subject device, thecuring cycle of the tyre, once the curing phase has been completed,comprises the additional phase of removing the dies from the aforesaidgeometric axis, to open the curing mould, guiding said dies by means ofindentations produced by the dies themselves in the tread band.

Further features and advantages shall become more readily apparent fromthe detailed description of a preferred but not exclusive embodiment ofa method and a device for curing tyres for vehicle wheels according tothe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The description shall be given below with reference to the accompanyingdrawings, provided purely by way of non-limiting indication, in which:

FIG. 1 is a diametrical section of a device according to the invention,with a tyre undergoing work closed in the moulding cavity;

FIG. 2 shows a semi-section of the device of FIG. 1 in an operativephase in which circumferential sectors of the curing mould disengage thetyre undergoing work;

FIG. 3 shows a semi-section of the device in an operative phase in whichthe detachment of tyre from the upper cheek of the curing mould iscarried out;

FIG. 4 shows a semi-section of the device in an operative phase in whichthe tyre is extracted from the lower portion of the mould;

FIG. 5 shows a phase whereby the tyre is laid onto a support plane withrollers;

FIG. 6 is an interrupted section taken according to the trace VI—VI ofFIG. 2

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the aforementioned drawings, the reference number 1indicates in its entirety a device for curing tyres for vehicle wheels,according to the present invention.

The device 1 comprises a curing mould 2 operatively housed in acontainment structure 3 and defining in its interior a moulding andcuring cavity 4 suitable to receive a tyre 5 undergoing work.

More in particular, the mould 2 essentially presents a lower cheek 6 andan upper cheek 7 mutually coaxial and able to operate on respectivesidewalls 5 a of the tyre 5, as well as a crown of radial sectors 8circumferentially distributed around a geometric axis Y—Y of themoulding cavity 4, coinciding with the axis of rotation of the tyre 5,and able to operate on a tread band 5 b of the tyre itself.

Within the moulding cavity, a curing bag of the usual kind (not shown)can operate, but in the preferential embodiment of the invention it ispreferred to omit such a bag which constitutes a disadvantageousobstacle to the transmission of heat towards the radially interiorsurface of the tyre.

For the purpose of locking the position of the tyre undergoing workwithin the moulding cavity, an upper gripping organ 30 and a lowergripping organ 31 are preferably associated to the lower cheek 6 andupper cheek 7, the gripping organs 30 and 31 can be activatedindependently of each other in any convenient way, to be brought from aresting position wherein their diametrical size is lesser than the innerdiameter of the bead of the tyre 5, to an operative condition whereinthey present a greater diametrical size than said diameter so that theyare able to hold respective beads 5 c of the tyre 5 in correspondencewith the inner circumferential edges of the respective lower cheek 6 andupper cheek 7.

Alternatively, the tyre undergoing work can be mounted on a rigidsupport (not shown) having the shape of the inner surface of the tyre,whereon the tire has preferably been constructed from the start byassembling the different components, for instance according to patentapplication EP 0 919 406 by the same Applicant.

The lower cheek 6 and upper cheek 7 are respectively fastened above abase portion 9 of the containment structure 3, and below a closureportion 10 of the containment portion itself. The sectors 8 are in turnengaged inside an annular portion 11 of the containment structure 3.

In a preferential embodiment of the invention, the curing mould 2 issubdivided into an upper portion 2 a and a lower portion 2 b able to bemutually approached to match substantially according to an equatorialmedian plane X—X of the moulding and curing cavity 4 and, hence, of thetyre 5 undergoing work.

For this purpose, each circumferential sector 8 presents an upperportion 8 a and a lower portion 8 b able to be coupled in a condition ofmutual contact on a median plane, preferably on the equatorial planeX—X.

The annular portion 11 of the containment structure 3 is in turnsubdivided in an upper semi-part 11 a and a lower semi-part 11 b,presenting respective upper 12 a, and lower 12 b, cone frustum shapedinner surfaces, symmetrically opposite and diverging towards theequatorial plane X—X. The upper semi-part 11 a of the annular portion 11forms, together with the closure portion 10, an upper containmentportion 3 a of the containment structure 3, whereas the lower semi-part11 b of the annular portion 11 defines, together with the base portion9, a lower containment structure 3 b of the containment structureitself.

The upper 3 a and lower 3 b containment portions are axially movablerelative to each other along the geometric axis Y—Y between a closedcondition wherein they match according to a diametrical plane, forinstance as shown in FIG. 1, and an open condition wherein they aremutually removed, for instance as shown in FIG. 4, to allow theoperations of loading and removing the tyre 5 from the moulding andcuring cavity 4. For this purpose it can for example be provided for theupper containment portion 3 a to be operatively engageable by a suitablelifting apparatus not shown herein as it is not relevant for thepurposes of the invention and achievable in any manner convenient to theperson versed in the art, for instance as described in patent EP0,459,375.

The illustrated embodiment also provides for the upper and lowercontainment portions 3 a and 3 b to be removably fastened relative toeach other in the closed condition by means of an annular bayonetclosure organ 13 operating on circumferential flanges 13 a provided incorrespondence with junction edges between the upper and lowercontainment portions themselves.

The presence of the annular bayonet closure organ 13 allows to maintainthe mould 2 in closed conditions during the tyre curing cycle andfurther allows, if necessary, to remove the entyre device 1 from asupport base 14, after disengaging removable coupling means 14 aoperating on the lower containment portion 3 b.

Each of the upper and lower portions 8 a and 8 b of the sectors 8 isslidingly guided, in any manner convenient for the person versed in theart, according to a generatrix of the respective upper interior conefrustum shaped surface 12 a, or lower interior cone frustum shapedsurface 12 b. The mobility of the upper portions 8 a and lower portions8 b of the sectors 8 along the interior cone frustum shaped surfaces 12a, 12 b is such that, following the mutual axial actuation of the upperand lower containment portions 3 a and 3 b, the upper and lower portionsof the sectors themselves are subject to translating between a closedposition wherein they are mutually approached and matching in thecircumferential direction to define the moulding and curing cavity 4,and an open condition wherein they are mutually removed both in theaxial direction and radially to the geometric axis Y—Y, to allow theinsertion and removal of the tyre 5.

In accordance with the present invention, each of the sectors 8comprises essentially a support body 15 operatively engaged in thecontainment structure 3 and bearing a plurality of moulding dies 16,preferably from one to four, each of which extends according to at leasta corresponding “pitch” of the tread design to be achieved on the tyre5, preferably a multiple of said pitch .

For purposes of the present description, the term “pitch” means acircumferential portion of the tread band 5 b of the tyre 5, comprisinga portion of tread design which repeats circumferentially identical toitself, for instance delimited by the distances between the centres oftwo consecutive homologous transverse grooves concurring in thedefinition of the tread design.

Advantageously, each support body 15 is subdivided into an upper portion15 a and a lower portion 15 b slidingly engaged respectively to theupper interior cone frustum shaped surface 12 a and to the lowerinterior cone frustum shaped surface 12 b of the upper and lowercontainment portions 3 a and 3 b. The upper portion 15 and lower portion15 b of each support body 15 are further guided in a direction radial tothe geometric axis Y—Y respectively by means of an upper sliding guide20 a and a lower sliding guide 19 a positioned peripherally relative tothe upper cheek 6 and lower cheek 7.

Each moulding die 16 is in turn subdivided into an upper portion 16 aand a lower portion 16 b respectively engaged to the upper portion 15 aand lower portion 15 b of the corresponding support body 15.

In a preferential embodiment, to each support body 15 is associated apair of moulding dies 16. In this circumstance, when a tyre 5 ismanufactured whose tread design presents, for instance, sixty-fourpitches, thirty-two support bodies 15 shall be provided, each subdividedinto a respective upper portion 15 and lower portion 15 b.

For the purposes of the present invention, the number of support bodies15 can, in any case, be equal or corresponding to a sub-multiple of thenumber of dies 16 and, hence, of the circumferential pitches comprisedin the tread design.

Each die 16, and more specifically each of the upper portions 16 a andlower portions 16 b composing it, is preferably engaged to therespective upper portion 15 a and lower portion 15 b of the support body15 with the possibility of sliding in circumferential direction. Forthis purpose, in dies 16, terminal projections 34 can be provided,slidingly guided in respective undercuts presented by the base body 15,all for instance as described in patent EP 0 451 832.

A FIG. 6 clearly shows, when the curing mould is in open conditions, andin any case when the sectors 8 are radially removed from the geometricaxis Y, each of the moulding dies 16 is distanced relative to thecircumferentially adjacent die according to a lesser measure than thedistance between two circumferentially contiguous support bodies 15.More in particular, it is provided for the distance measurable betweentwo circumferentially contiguous support bodies 15 to be at least equalto the distance measurable on average between two contiguous dies 16,multiplied times the number of dies associated to each support body 15.In this way, one has the certainty that when the sectors 8 are radiallyapproached in the closed condition, each moulding die 16 perfectlymatches the circumferentially adjacent dies without any chance that apremature interference between the circumferentially contiguous supportbodies 15 may prevent the correct closure of the mould 2.

The presence of a number of dies 16 corresponding to the number ofpitches comprising the tread design and movable in a mutuallyindependent manner in the direction of circumferential development,assures that when the mould 2 is closed each matrix 16 penetrates thetread band 5 b of the tyre 5 according to a direction perfectly radialto the geometric axis Y—Y. In this way it is certain that no anomalousstresses and/of deformations are imparted to the raw elastomericmaterial constituting the tread band 5 b, as would instead be the casewith the use of traditional moulds with eight or sixteen dies, ofrelatively high circumferential extension. Moulds of this kind cannotconfer a perfectly radial actuation trajectory to all parts destined toform the tread band, causing physical and structural inconsistencies inthe finished tyre which translate into performance shortfalls by thetyre. In particular, one of the most significant drawbacks isconstituted by the characteristic rolling noisiness of the tyre,identified by persons versed in the art with the definition of “eighthharmonic”.

It should further be noted that the subdivision of the sectors 8 of themould 2 into an upper portion 8 a and a lower portion 8 b allowsconsiderably to limit the radial excursion necessary to the sectorsthemselves to allow the introduction and removal of the tyre 5. Inpractice, the radial excursion of the sectors 8, and more in particularof each of their portions 8 a, 8 b, can advantageously be limited to theamount necessary to achieve the penetration of the ribs, present on themoulding dies 16, into the tread band 5 b according to the desireddepth.

The vulcanising unit 1 further comprises heating devices able to applyheat to the tyre 5, both from its interior and from its exterior, todetermine its correct curing.

For the purposes of administering heat inside the tyre 5, the heatingdevices can for instance comprise a steam injection conduit 17 and asteam extraction conduit 18 communicating with the interior of thecuring bag 4 to inject, and respectively, remove steam therefrom.

For the purposes of administering heat from the exterior of the tyre 5,the heating devices further comprise a lower hot table 19 locatedadjacently to the lower cheek 6, an upper hot table 20 locatedadjacently to the upper cheek 7, and at least an annular hot table 21 a,21 b positioned around the circumferential development of the mouldingand curing cavity 4, concentrically to the geometric axis Y—Y.

The lower hot table 19 and the upper hot table 20 are axially movable inthe respective lower and upper containment portions 3 b and 3 a todetermine the radial removal of the lower portions 8 b and upperportions 8 a of the sectors 8 following the mutual axial removal of theupper and lower containment portions 3 a and 3 b. For this purpose thelower hot table 19, peripherally bearing the aforesaid lower slidingguides 19 a, is constantly maintained against the lower cheek 6 by meansof lower thrust springs 22 or equivalent elastic means operating betweenthe lower cheek itself and the base portion 9 of the containmentstructure 3. Similarly, the upper hot table 20, peripherally bearing theaforesaid upper sliding guides 20 a, is constantly maintained againstthe upper cheek 7 by means of upper thrust springs 23 or equivalentelastic means operating between the hot table itself and the closureportion 10 of the containment structure 3.

The annular hot table 21 a, 21 b is in turn preferably integrated in thestructure of the annular portion 11 of the containment structure 3, andis essentially defined by a lower annular cavity 21 a and an upperannular cavity 21 b obtained respectively in the upper semi-part 11 aand in the lower semi-part 11 b of the annular portion itself.

The aforementioned heating devices further comprise steam supplyingmeans routed into the lower hot table 19, upper hot table 20 andcircumferential hot table 21 a, 21 b.

According to the present invention, the steam supplying means, notdescribed in detail herein since they can be embodied in any mannerconvenient to the person versed in the art, are able to supply into thelower hot table 19, and into the lower cavity 21 a of the annular hottable, steam at higher temperature than the steam supplied into theupper hot table 20 and into the upper annular cavity 21 b of the annularhot table itself.

More specifically, in a preferential embodiment the steam supplied intothe lower hot table 19 presents a temperature ranging between 155° C.and 165° C., whereas the temperature of the steam supplied into theupper hot table 20 ranges between 148° C. and 158° C.

For purposes of supplying steam at differentiated temperatures, it ispreferably provided for the upper annular cavity 21 b of thecircumferential hot table to be in fluid communication with the upperhot table 20, whilst the lower annular cavity 21 b of thecircumferential hot table is in fluid communication with the lower hottable 19.

Externally to the containment structure 3, and more specifically on eachof the upper semi-part 11 a and lower semi-part 11 b of the annularportion 11, a first and a second fluid-dynamic junction elements 24, 25are provided, whereto respective steam delivery pipelines (not shown),coming from the aforementioned steam supply means, can be engaged.

The steam injected into the lower annular cavity 21 a of thecircumferential hot table 21 a, 21 b is transferred into the lower hottable 19 through a first junction pipeline indicated by the dashed line26.

Similarly, the steam injected into the upper annular cavity 21 b of thecircumferential hot table 21 b is transferred into the upper hot table20 through a second junction pipeline indicated by the dashed line 27.

A first and a second output junction 28, 29 allow the evacuation of thesteam respectively from the lower hot table 19 and from the upper hottable 20.

It should be noted that the supply of the steam at differenttemperatures respectively for the upper portion 2 a and for the lowerportion 2 b of the mould 2 determines an unexpected homogeneity in thedelivery of heat between the different components of the mould itselfand especially to the tyre 5 undergoing work.

The Applicant has become aware that an appreciable portion of the heatdissipated by the lower hot table 19, as well as by the lower annularcavity 21 a of the circumferential hot table 21 a, 21 b is transmittedto the upper portion 2 a of the mould 2 through the natural tendency ofhot air to rise.

Moreover, the higher temperature of the steam injected into the lowerportion 2 b of the mould 2 compensates for the heat dissipation from thelower cheek 6 and from the lower portions 8 b of the sectors 8,particularly considerable when replacing the tyre 5 undergoing work,when the vulcanising unit 1 remains completely open in the absence ofthe tyre itself.

After the above description, prevalently structural, the operation ofthe curing device according to the present invention shall be describedbelow.

Simultaneously with the closure of the tyre 5 undergoing work within themould 1, steam is supplied into the lower hot table 19, upper hot table20 and circumferential hot table 21 a, 21 b as described previously, todetermine a homogeneous administration of heat through the outersurfaces of the tyre itself.

At the same time, steam is injected into the interior of the mouldingand curing cavity 4, to provide heat also through the inner surfaces ofthe tyre 5. Throughout the entyre curing cycle, the beads 5 c of thetyre 5 are withheld against the internal circumferential edges of therespective cheeks 6, 7: in the embodiment of the vulcanising unit shownin the figures, this holding action is effected by means of the upperand lower gripping means 30 and 31, both readied in operative conditionbefore beginning the injection of steam into the moulding and curingcavity 4.

The injection of steam into the moulding and curing cavity 4 can befollowed, after a predetermined time, by the injection of an inert gassuch as high-pressure nitrogen, to assure the perfect penetration of thetread band 5 b of the tyre 5 by the moulding dies 16.

Once the curing cycle, which can require a time ranging between 10 and30 minutes, depending on the dimensions and structure of the tyre to becured, is complete, the inert gas and the vapours still present in themoulding and curing cavity 4 are evacuated therefrom, and the bayonetclosure organ 13 is rotated angularly to allow the opening of the mould2 by the lifting of the upper portion 3 a of the containment structure3.

In an initial phase of this lifting operation, as shown in FIG. 2, theupper and lower thrust springs 23 and 22 cause the upper and lower hottables 20 and 19 to move away from the respective closure portion 10 andbase portion 9 of the containment structure 3, causing the sliding ofthe upper portions 8 a and of the lower portions 8 b of the sectors 8 onthe internal cone frustum shaped inner surfaces 12 a, 12 b of theannular portion 11.

In this situation, the sectors 8 move radially away from the axis Y—Y,causing the moulding dies 16 to disengage from the tread band 5 b of thetyre 5, whilst the upper and lower portions 8 a and 9 b of the sectorsthemselves, by effect of the upper springs 23 and of the lower springs22, are maintained in mutual contact (FIG. 2) and in mutually oppositethrusting relationship.

Simultaneously with the initial removal phase of the upper portion 3 aof the containment structure 3, the upper gripping organ 30 is broughtto a resting condition to free the upper bead 5 c of the tyre 5, whilstthe lower gripping organ 31 maintains the lower bead engaged on thelower cheek 6.

Therefore, with the further lifting of the upper portion 3 a of thecontainment structure 3, and the consequent move of the upper portion 2a away from the lower portion 2 b of the mould 2, the detachment of thetyre 5 from the upper cheek 7 is brought about, as per FIG. 3.

Once this operation has been completed, the upper containment structure3 a is lowered again until the upper portions 8 a of the sectors 8 areagain brought in contact on the respective lower portions 8 b, whereuponthe upper gripping organ 30 is again brought in operative condition tohold the upper bead 5 c of the tyre 5 against the upper cheek 7.

The lower gripping organ 31 is in turn brought to the resting conditionby freeing the lower bead 5 c of the tyre 5 in such a way that the tyreitself is able to be detached from the lower cheek 6 and extracted fromthe lower portion 3 b of the containment structure 3 as a result of thenew lifting of the upper portion 3 a, as shown in FIG. 4.

The upper portion 3 a of the containment structure 3 is therefore ableto be translated laterally relative to the lower portion 3 b in such away that the tyre 5, previously detached from the upper cheek 7, can belaid on a roller bed 33 or other suitable collection means, followingthe translation of the upper gripping organ 30 in the resting conditionafter the lowering of the upper portion 3 a or of the upper grippingorgan alone, as shown in FIG. 5

Once the cured tyre is released on the roller bed 33, the device 1 isready to receive in engagement a new tyre to be cured which, through anymeans suitable for the purpose, will be positioned coaxially with itsown upper bead 5 c above the upper gripping organ 30. The latter shallsubsequently be brought to the operative condition to engage the bead 5c of the new tyre 5 against the inner circumferential border of theupper cheek 7.

The upper portion 3 a of the containment structure 3, after having beencoaxially brought back above the lower containment portion 3 b, shall belowered thereon, to determine the closure of the new tyre 5 in the mould2.

The present invention achieves important advantages.

The provision of steam at differentiated temperatures respectively forheating the upper and lower part of the mould allows an optimaldistribution of the heat administered to the tyre which advantageouslybrings about a high degree of uniformity of the cured tyre and of itsoperating performance.

The method according to the invention originates from the intuition thatthe lower hot table must be supplied with steam at a determinedtemperature corresponding with that necessary for a correct curing ofthe lower sidewall and that the upper hot table must be supplied withsteam at a lower temperature according to a predetermined quantity tothat the difference between the two temperatures is substantiallycompensated for by the inflow of heat transferred and emitted upwards bythe lower part of the vulcanising unit.

Advantageously the difference between the temperatures at which thesteam is supplied to the cheeks of the mould translates into auniformity of characteristics and performance for the two sidewalls ofthe tyre.

Moreover, very favourably, the higher temperature of the steam injectedinto the lower portion 2 b of the mould 2 compensates for thedissipation of heat from the lower cheek 6 and from the lower portions 8b of the sectors 8, particularly considerable when replacing the tyre 5undergoing work, when the device 1 remains completely open in theabsence of the tyre itself.

By way of non limiting indication, it is specified that the Applicanthas found particularly advantageous the modification of the temperatureof the fluids of the curing cycle, normally carried out, as indicatedbelow, in accordance with the invention and with reference to a curingpress equipped with curing bag, for curing tyres ranging in size from185/65R15 and 254/40R18.

TABLE 1 Temperatures for Temperatures for Invention Devices Prior ArtMethod (° C.) Method (° C.) Curing Bag 200 200 Upper Annular Hot 180 156Table Lower Annular Hot 180 159 Table Lower Cheek Hot Table 160 159Upper Cheek Hot Table 160 156 Cycle Duration (min.) 14′-25′ 10′-19′Energy Consumption 2100  1500  (kcal/kg)

The results of bench and road tests confirm, through the high degree ofhomogeneity and uniformity of the structural and behaviouralcharacteristics of the tyres, the excellent distribution of the heatadministered to the tyre achieved with the provision of steam atdifferentiated temperatures respectively for heating the upper and thelower part of the mould 2.

In particular, the homogeneity of the distribution of heat on theopposite sidewalls of the tyre is greatly improved, overcoming thelimitations of the state of the art where, in spite of the contrivancesadopted to try to obtain a temperature of the curing fluid that isexactly identical between the lower hot table and the upper hot table,it was always difficult to obtain the same degree of curing on the twosidewalls of the tire: the one situated superiorly always had a tendencyto be over-cured relative to the sidewall situated inferiorly.

It should further be noted that, advantageously, the lower temperatureof the steam supplied into the two tables translates into less energyconsumption per tyre and per vulcanising unit, quite appreciable inrelation to the number of curing devices simultaneously in use.

The optimisation of the distribution of the head transferred through themould allows to achieve considerable improvements in terms of caloricexpenditure, thanks to the additional constructive peculiarities of thesubject device.

It should be noted, in fact, that the construction of the mould 2 and ofthe containment structure 3 in two semi-parts subdivided on theequatorial plane allows to minimise, as stated, the radial excursionthat the sectors 8 must perform during the opening phase to allow theremoval and reintroduction of the tires undergoing work.

In this situation the sectors remain very close to each other even whenthe device is fully open, thereby avoiding excessive heat losses, whichdo instead take place in the moulds constructed according to the priorart, wherein the sectors are obtained in a single piece and connected toa sole sector-bearing ring so that they are considerably distanced fromeach other when the vulcanising unit is open.

The constructive features adopted in the realisation of the sectorsfurther confer a reduced thermal inertia to the sectors themselves,which reduced thermal inertia is also allowed by the containment of heatdissipation during the opening phase. Exploiting this reduced thermalinertia in an original and advantageous manner, the invention proposesto supply the portions of the annular hot table with steam at the sametemperature (with the same steam) as the steam injected into the upperand lower hot tables, thereby eliminating the need to provide anadditional supply of steam at different temperatures for the annular hottable.

1. A method for curing a tyre, comprising the steps of: closing the tyrein a mould; heating a lower hot table to transmit heat to the tyre;heating an upper hot table to transmit heat to the tyre; and heating anannular hot table to transmit heat to the tyre; wherein the lower hottable, the upper hot table, and the annular hot table are associatedwith the mould, wherein the annular hot table is thermally-connected toa circumferential development of the mould, and wherein a quantity ofheat provided to the lower hot table is greater than a quantity of heatprovided to the upper hot table.
 2. The method of claim 1, wherein aquantity of heat provided to a lower portion of the annular hot table isgreater than a quantity of heat provided to an upper portion of theannular hot table.
 3. The method of claim 1, wherein the quantity ofheat provided to the lower hot table is greater than the quantity ofheat provided to the upper hot table, and wherein a quantity of heatprovided to a lower portion of the annular hot table is greater than aquantity of heat provided to an upper portion of the annular hot table.4. The method of claim 1, wherein a heating fluid is supplied to thelower hot table.
 5. The method of claim 1, wherein a heating fluid issupplied to the upper hot table.
 6. The method of claim 1, wherein aheating fluid is supplied to the annular hot table.
 7. The method ofclaim 1, wherein a first heating fluid is supplied to the lower hottable, and wherein a second heating fluid is supplied to the upper hottable.
 8. The method of claim 7, wherein a temperature of the firstheating fluid is greater than a temperature of the second heating fluid.9. The method of claim 8, wherein the temperature of the first heatingfluid is between 155° C. and 165° C.
 10. The method of claim 8, whereinthe temperature of the second heating fluid is between 148° C. and 158°C.
 11. The method of claim 7, wherein the first heating fluid comprisesdry, saturated steam, or wherein the second heating fluid comprises dry,saturated steam, or wherein the first heating fluid comprises dry,saturated steam and the second heating fluid comprises dry, saturatedsteam.
 12. The method of claim 1, wherein a first heating fluid issupplied to the lower hot table, wherein a second heating fluid issupplied to the upper hot table, and wherein a third heating fluid issupplied to the annular hot table.
 13. The method of claim 12, wherein atemperature of the first heating fluid is greater than a temperature ofthe second heating fluid.
 14. The method of claim 13, wherein thetemperature of the first heating fluid is between 155° C. and 165° C.15. The method of claim 13, wherein the temperature of the secondheating fluid is between 148° C. and 158° C.
 16. The method of claim 15,wherein the first heating fluid comprises dry, saturated steam, orwherein the second heating fluid comprises dry, saturated steam, orwherein the first heating fluid comprises dry, saturated steam and thesecond heating fluid comprises dry, saturated steam.
 17. The method ofclaim 1, wherein a first heating fluid is supplied to a lower portion ofthe annular hot table, and wherein a second heating fluid is supplied toan upper portion of the annular hot table.
 18. The method of claim 17,wherein a temperature of the first heating fluid is greater than atemperature of the second heating fluid.
 19. The method of claim 18,wherein the temperature of the first heating fluid is between 155° C.and 165° C.
 20. The method of claim 18, wherein the temperature of thesecond heating fluid is between 148° C. and 158° C.
 21. The method ofclaim 17, wherein the first heating fluid comprises dry, saturatedsteam, or wherein the second heating fluid comprises dry, saturatedsteam, or wherein the first heating fluid comprises dry, saturated steamand the second heating fluid comprises dry, saturated steam.
 22. Themethod of claim 1, wherein a heating fluid is supplied to the lower hottable, and wherein the heating fluid also is supplied to a lower portionof the annular hot table.
 23. The method of claim 22, wherein atemperature of the heating fluid is between 155° C. and 165° C.
 24. Themethod of claim 22, wherein the heating fluid comprises dry, saturatedsteam.
 25. The method of claim 1, wherein a heating fluid is supplied tothe upper hot table, and wherein the heating fluid also is supplied toan upper portion of the annular hot table.
 26. The method of claim 22,wherein a temperature of the heating fluid is between 148° C. and 158°C.
 27. The method of claim 22, wherein the heating fluid comprises dry,saturated steam.
 28. The method of claim 1, wherein a first heatingfluid is supplied to the lower hot table, wherein a second heating fluidis supplied to the upper hot table, wherein the first heating fluid alsois supplied to a lower portion of the annular hot table, and wherein thesecond heating fluid also is supplied to an upper portion of the annularhot table.
 29. The method of claim 28, wherein a temperature of thefirst heating fluid is greater than a temperature of the second heatingfluid.
 30. The method of claim 29, wherein the temperature of the firstheating fluid is between 155° C. and 165° C.
 31. The method of claim 29,wherein the temperature of the second heating fluid is between 148° C.and 158° C.
 32. The method of claim 28, wherein the first heating fluidcomprises dry, saturated steam, or wherein the second heating fluidcomprises dry, saturated steam, or wherein the first heating fluidcomprises dry, saturated steam and the second heating fluid comprisesdry, saturated steam.
 33. A method for curing a tyre, comprising thesteps of: closing the tyre in a mould; heating at least one lower hottable to transmit heat to the tyre; heating at least one upper hot tableto transmit heat to the tyre; and heating at least one annular hot tableto transmit heat to the tyre; wherein the at least one lower hot table,the at least one upper hot table, and the at least one annular hot tableare associated with the mould, wherein the at least one annular hottable is thermally-connected to a circumferential development of themould, and wherein a quantity of heat provided to the at least one lowerhot table is greater than a quantity of heat provided to the at leastone upper hot table.
 34. A method for curing a tyre, comprising thesteps of: closing the tyre in a mould; transmitting heat to the tyre;opening the mould; and removing the tyre from the mould; wherein themould comprises a cavity at least partly delimited by a lower cheek, anupper cheek, and a plurality of moulding dies, wherein the lower cheekis thermally-connected to at least one lower hot table, wherein theupper cheek is thermally-connected to at least one upper hot table,wherein the plurality of moulding dies is thermally-connected to atleast one annular hot table, wherein the at least one annular hot tableis thermally-connected to a circumferential development of the mould,wherein the step of closing the tyre in the mould comprises decreasing adistance between the lower cheek and the upper cheek, wherein the stepof closing the tyre in the mould further comprises moving the pluralityof moulding dies toward a rotation axis of the tyre, wherein the step oftransmitting heat to the tyre comprises providing quantities of heat tothe at least one lower hot table, the at least one upper hot table, andthe at least one annular hot table, wherein the quantity of heatprovided to the at least one lower hot table is greater than thequantity of heat provided to the at least one upper hot table, whereinthe step of opening the mould comprises increasing the distance betweenthe lower cheek and the upper cheek, and wherein the step of opening themould further comprises moving the plurality of moulding dies away fromthe rotation axis of the tyre.
 35. The method of claim 34, whereinindentations in a tread band of the tyre at least partly guide movingthe plurality of moulding dies away from the rotation axis of the tyre.36. An apparatus for curing a tyre, comprising: a mould; a lower hottable; an upper hot table; an annular hot table; and devices forsupplying one or more first heating fluids to the lower hot table, theupper hot table, and the annular hot table; wherein the mould comprisesa cavity, wherein the lower hot table is thermally-connected to a lowercheek of the mould, wherein the upper hot table is thermally-connectedto an upper cheek of the mould, wherein the annular hot table isthermally-connected to a circumferential development of the mould, andwherein a temperature of the one or more first heating fluids suppliedto the lower hot table is greater than a temperature of the one or morefirst heating fluids supplied to the upper hot table.
 37. The apparatusof claim 36, wherein the annular hot table comprises a lower portion andan upper portion.
 38. The apparatus of claim 37, wherein a temperatureof the one or more first heating fluids supplied to the lower portion ofthe annular hot table is greater than a temperature of the one or morefirst heating fluids supplied to the upper portion of the annular hottable.
 39. The apparatus of claim 37, wherein the lower portion of theannular hot table is in fluid communication with the lower hot table.40. The apparatus of claim 37, wherein the upper portion of the annularhot table is in fluid communication with the upper hot table.
 41. Theapparatus of claim 36, further comprising: a first conduit for injectinga second heating fluid into an interior of the cavity; and a secondconduit for extracting the second heating fluid from the interior of thecavity.
 42. The apparatus of claim 37, wherein a lower containmentportion of a containment structure comprises the lower portion of theannular hot table, wherein an upper containment portion of thecontainment structure comprises the upper portion of the annular hottable, and wherein a distance between the containment portions in anopen condition is greater than the distance between the containmentportions in a closed condition.
 43. The apparatus of claim 36, wherein alower containment portion of the mould comprises a plurality of lowerradial sectors, wherein an upper containment portion of the mouldcomprises a plurality of upper radial sectors, wherein, in a dosedcondition of the containment portions, the lower and upper radialsectors are circumferentially distributed about a geometric axis of thecavity, wherein each of the radial sectors comprises a support bodyslidingly engaged to a corresponding containment portion, wherein, in anopen condition of the containment portions, the radial sectors areaxially-distant from a rotation axis of the tyre, wherein, in a closedcondition of the containment portions, the radial sectors areaxially-close to the rotation axis of the tyre, wherein, in a closedcondition of the containment portions, the radial sectors at leastpartly delimit the cavity, and wherein each sector comprises at leastone moulding die removably engaged to the respective support body. 44.The apparatus of claim 43, wherein each sector comprises at least twomoulding dies removably engaged to the respective support body.
 45. Theapparatus of claim 43, wherein each of the moulding dies comprises acircumferential extension corresponding to a pitch of a tread design tobe defined on the tyre.
 46. The apparatus of claim 43, wherein, in aclosed condition of the containment portions, the lower radial sectorscontact the upper radial sectors substantially near an equatorial planeof the cavity.
 47. An apparatus for curing a tyre, comprising: a mould;at least one lower hot table; at least one upper hot table; at least oneannular hot table; and devices for supplying one or more heating fluidsto the at least one lower hot table, the at least one upper hot table,and the at least one annular hot table; wherein the mould comprises acavity, wherein the at least one lower hot table is thermally-connectedto a lower cheek of the mould, wherein the at least one upper hot tableis thermally-connected to an upper cheek of the mould, wherein the atleast one annular hot table is thermally-connected to a circumferentialdevelopment of the mould, and wherein a temperature of the one or moreheating fluids supplied to the at least one lower hot table is greaterthan a temperature of the one or more heating fluids supplied to the atleast one upper hot table.